Active-type liquid crystal displays and organic electroluminescence displays are formed on glass substrates. Pixels arranged in the form of a matrix on a glass substrate are controlled by transistors disposed in the vicinity of the pixels. Since it is difficult to form a transistor made of a semiconductor single crystal on a glass substrate, a thin-film transistor (TFT) using amorphous silicon or polysilicon is used for controlling the pixels. A TFT has an advantage in that it can be formed on a substrate having a large area at low cost. It has, however, a problem that it cannot operate at high speed due to its low mobility compared with crystalline silicon. A TFT has another problem that materials to be used for a substrate are limited because the substrate has to be kept at high temperature in forming a semiconductor film thereon. In order to solve these problems, a method of using silicon pieces taken out of an SOI substrate as transistor channel regions has been proposed (see “A printable form of silicon for high performance thin film transistors on plastic substrates”, Applied Physics Letters, vol. 84, 2004, pp. 5398).
According to this method, the process begins by forming patterns on an SOI layer so that each pattern has a larger area than a channel region. Next, silicon pieces are separated from the substrate by wet etching with hydrofluoric acid. Then, the silicon pieces are collected from the hydrofluoric acid and disposed respectively between source electrodes and drain electrodes. Thus, a thin-film transistor is formed. The channel region of this transistor is formed of single crystal silicon. Therefore, this method makes it possible to form a transistor with a mobility exceeding 100 cm2V−1s−1.
However, according to the above-mentioned conventional method in which silicon pieces are formed from an SOI substrate, it is difficult to freely change the thickness of the silicon pieces. In addition, there is another problem that the cost of the SOI substrate is high. There is still another problem in the conventional manufacturing method that only a limited number of silicon pieces can be produced from a single SOI substrate.